Rice cooker inserts provide a particularly challenging opportunity for non-stick or release coatings.
Such inserts are generally deep drawn from aluminum alloy and are anodized to provide a durable, attractive finish on the outside. Such inserts are used in electrically heated rice cookers which may be kept hot for many hours in the day or even continuously in residential kitchen use. In the presence of steam generated in the rice, starch from the rice and any other ingredients used tend to stick tenaciously to the insert.
Presently available coatings for rice cooker inserts tend to crack during deep drawing, to develop stains from oils and water in manufacture and use, and to develop blisters during use. Such coatings include clear polytetrafluoroethylene applied in a single coat to an electrolytically etched aluminum alloy blank or disc and rolled or pressed into the surface of the disc, before deep drawing of the insert.
Superior coating systems are desirable. Although good coating technology is known, including the primers of U.S. Pat. Nos. 4,011,361 - Vassiliou et al. (Mar. 8, 1977) and 4,049,863 - Vassiliou (Sept. 20, 1977), and the systems of 4,169,083 (Sept. 25, 1979), 4,180,609 (Dec. 25, 1979), and 4,353,950 (Oct. 12, 1982) - all to Vassiliou, optimum integrated coating systems for rice cookers are not known. These patents are incorporated herein by reference.